The present invention relates to an anode containing a binder and a battery using it.
In recent years, electronic devices commencing with a mobile phone and a notebook computer have become cordless and portable. Thin, small-sized, and light weight portable electronic devices have been developed one right after the other. Further, as the devices have become diversified, the power source usage amount has been increased. Therefore, high capacity of batteries, which is the energy source of these electronic devices, particularly of secondary batteries has been increasingly demanded.
As a secondary battery used in the past, there are a lead battery, a nickel cadmium battery and the like. Currently, a nickel hydrogen battery and a lithium ion secondary battery are in practical use.
Of the foregoing, the lithium ion secondary battery has a structure as follows, for example. A cathode in which LiCoO2 as the cathode active material, graphite as an electrical conductor, and a binder such as polyvinylidene fluoride are layered together on a cathode current collector made of an aluminum thin plate; and an anode in which an anode active material such as carbon, cokes, and graphite and a binder are layered on an anode current collector made of a copper thin plate are layered with a thin film separator made of polypropylene, polyethylene or the like inbetween (for example, refer to Japanese Unexamined Patent Application Publication No. H08-315817).
Further, a polymer lithium ion secondary battery having a sandwich structure in which an electrolyte gelated by polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride or the like is filled between an electrode and a separator has been in practical use.
When such a lithium ion secondary battery suffers damage from outside, Joule heat is generated by short circuit in the damaged section, and battery temperatures are increased. In this case, a current is blocked by a safety mechanism such as shutdown function by the separator. However, as described above, when polyvinylidene fluoride is used as a binder for the anode, there is a disadvantage that the battery temperatures are more increased due to exothermic reaction between fluorine contained in the polyvinylidene fluoride and lithium inserted in the anode.